The present invention relates to an electro-luminescent (EL) element and a lighting unit employing the same EL element.
Electronic apparatuses, including cellular phones and personal computers, have been equipped with various and better functions. Thus, EL element and lighting units used in such electronic apparatuses have been subject to a variety of requirements.
A conventional EL element is described hereinafter with reference to FIG. 8 and FIG. 9. FIG. 8 shows a sectional view of a conventional EL element. FIG. 9 is a perspective view illustrating respective layers laminated. The EL element comprises the following elements:
(a) transparent insulating base 1;
(b) transparent electrode layer 2 formed by printing an indium tin oxide (ITO) film or transparent synthetic resin film on the entire lower face of base 1;
where the ITO film is formed by a sputtering method or a electron beam evaporation method, and the optically transparent film is formed by printing transparent synthetic resin in which indium tin oxide is dispersed,
(c) light emitting layer 3 formed by dispersing zinc sulfide base material of light emission into synthetic resin;
(d) dielectric layer 4 formed by dispersing barium titanate into synthetic resin;
(e) back-electrode layer 5 made of silver or carbon-resin composite; and
(f) insulating layer 6 made of epoxy resin or polyester resin.
The elements (c), (d) and (e) are printed beneath element (b) in this order sequentially, and then element (f) is disposed beneath element (e) to cover all the elements.
The EL element structured above is disposed beneath a plurality of pushbuttons or a display device such as LCD, so that the EL element is used for illuminating an operating section or the display device of a lighting unit.
When a voltage is applied between transparent electrode layer 2 and back electrode layer 5, an entire surface of light emitting layer 3 disposed between layer 2 and layer 5 emits light. This light illuminates the pushbuttons or the display devices from their backs.
In the conventional EL element discussed above, the structure allows the entire EL element to emit light, so that the EL element can illuminate a plurality of pushbuttons or display devices simultaneously, i.e., overall lighting is achievable. However, this structure cannot illuminate only a specified pushbutton or a specified spot on the display device, i.e., partial lighting is not achievable. Therefore, a plurality of light-emitting elements such as EL elements or LEDs are desirably combined for achieving partial lighting. This structure, however, needs more components and increases the cost.
An EL element in accordance with an exemplary embodiment of the present invention comprises the following elements:
a light transmitting base;
a front electrode layer formed beneath the base;
a light-emitting layer formed beneath the front electrode layer; and
a back electrode layer formed beneath the light-emitting layer.
The front electrode layer includes light transmitting front electrodes forming respective lines and front wiring-electrodes which couples the light transmitting front electrodes with each other. The back electrode layer includes back electrodes forming respective lines and back wiring-electrodes which couples the back electrodes with each other. The lines of the light transmitting front electrodes are overlaid above the lines of the back electrodes at a given angle via the light-emitting layer. The plural electrodes are coupled with each other by the wiring-electrodes to form a matrix, so that plural light-emitting pixels are formed. This structure allows a specified pixel to emit light or plural pixels to emit light simultaneously. As a result, a variety of lighting can be realized by this EL element.